Due to trends towards higher bandwidth demands and advances in the WDM device technology, WDM PONs are considered to be promising candidates for next-generation broadband access networks.
Besides, the growing popularity of mobile data services is also placing increasing demands on backhaul. WDM-PONs are able to provide symmetrical ultra-high bandwidth to base stations and hence can easily address the growing capacity needs of mobile backhaul. Faults occur in PONs, e.g. due to breaks in an optical fiber or due to a deteriorating or non-functioning optical line terminal (OLT) or optical network terminal (ONT). In order to shorten the service provision down-time caused by a failure in a PON, effective monitoring should be applied enabling fault detection and fault localization.
FIG. 1 presents an exemplary WDM-based PON enabling monitoring. The WDM-based PON comprises a central office (CO) 100, a remote node (RN) 102 and multiple ONTs 104a-n. The CO 100 comprises an OLT 106, an optical time domain reflectometry (OTDR) device 108, as well as an external wavelength adaptation module (EWAM) 110 and a wavelength filter 112.
The OTDR device 108 generates a monitoring signal that can be wavelength adapted or tuned in EWAM 110 and in the wavelength filter 112 after it is provided to the RN 102 and further to the ONTs 104a-n of the WDM-PON. The RN 102 distributes the monitoring signal via drop fibers to the ONTs based on the wavelength of the monitoring signal. Any reflection and/or scattering by the WDM-PON is returned towards the CO and the OTDR-device, based on which the WDM-PON can be supervised.
High connection availability and low failure impact by any single failure is required, in particular for business access and mobile backhauling. For this reason, protection of feeder fibers (FFs) is often a main task by operators.
FIG. 2 schematically presents a WDM-PON architecture with a plurality of COs 100a-c connected to a RN 114 via disjoint FFs 116a-c. This architecture supports open access since a user can choose a service from any CO. These COs are generally geographically spread. Each CO has an OLT for sending data in the WDM-based PON.
FIG. 3 schematically presents another WDM-PON architecture with a single CO 100 having a plurality of OLTs 106a-c connected to a RN via joint FFs 116. This architecture supports resilience since several FFs are provided from one and the same CO.
In order to provide connection protection and improved reliability, FIGS. 2 and 3 present WDM-PON architectures with multiple FFs.
By providing a plurality of different COs open access is enabled for customers. This promotes competition and market diversity, as this concept means a degree of freedom in the network architecture to offer a choice of services to residential and business users. For instance, open access allows users to select one out of a plurality of different service/network providers.
The schematically presented WDM-PONs of FIGS. 2 and 3, provide open access on a wavelength level. Within these architectures, the users can freely choose the service among the available service providers (SPs)/network providers (NPs) by selecting a certain wavelength. This idea for open access may be extended to any type of WDM-based PONs, e.g. hybrid WDM/time division multiplexing (TDM) PON.
However, the supervision mechanism as presented in FIG. 1 cannot be directly applied to the PON architectures with multiple FFs as presented in FIGS. 2 and 3, i.e. for open access and resilience.
There is therefore a need for enabling an improved monitoring of a WDM-based PON with multiple FFs.